1. Field of the Invention
The present invention relates to novel thermosetting compositions, thermal latent catalysts, methods of coating and coated articles. More particularly, it relates to novel thermosetting compositions having excellent chemical properties, physical properties, weathering resistance and storage stability and methods of coating to provide a top coating having the excellent properties as described above and excellent appearance by using the thermosetting compositions as the top coating material.
2. Description of the Prior Art
It is generally known that thermosetting compositions can be prepared from compounds having carboxyl groups and compounds having reactive functional groups which can form chemical bonds with the carboxyl groups by heating, such as epoxy group, oxazoline group, silanol group, alkoxysilane group, hydroxyl group, amino group, imino group, isocyanate group, blocked isocyanate group, cyclocarbonate group, vinyl ether group, vinyl thioether group, aminomethylol group, alkylated aminomethylol group, acetal group and ketal group. The thermosetting compositions give cured products having excellent chemical properties, physical properties and weathering resistance and are widely utilized in the field of coating composition, ink, adhesive and molded plastics.
As thermosetting compositions described above, for example, compositions comprising combinations of carboxyl group and epoxy group have been disclosed in Laid Open Japanese Patent Application Showa 51-114429, Laid Open European Patent Application 29595 and U.S. Pat. Nos. 4371667, 4650718, 4681811, 4703101 and 4764430.
Compositions comprising combinations of carboxyl group and oxazoline group, as other examples, have been disclosed in U.S. Pat. No. 3505297 and Laid Open Japanese Patent Applications Showa 60-88038 and Heisei 2-115238.
The thermosetting compositions give cured products having excellent chemical properties, physical properties and weathering resistance and are widely utilized in the field of coating composition, ink, adhesive and molded plastics.
However, the reactivity between the carboxyl group and the reactive functional groups is generally very high and compositions in which compounds having carboxyl groups and compounds having the reactive functional groups are mixed together have a problem that the compositions are often gelled during storage and the period suitable for service is short.
Compounds comprising carboxyl groups conventionally utilized for thermosetting compositions described above have problems that solubility to generally used solvents is low and that compatibility with the compounds having reactive groups with the carboxyl group is inferior because of the tendency of the carboxyl group to form strong hydrogen bonds. When thermosetting compositions comprising these kinds of compounds are utilized as top coating materials, they naturally have problems that preparation of high solid coating materials is difficult and that appearance of the finished coating is inferior.
For the purpose of solving these problems, it was proposed that carboxyl group was blocked by converting it to tertiary-butyl ester and the free carboxyl group was regenerated by elimination of isobutene by heating (Laid-Open Japanese Patent Application Heisei 1-104646). However, this method required a high temperature, such as 170.degree.-200.degree. C., for the heat decomposition of the tertiary-butyl ester and pock marks which were made by foaming and degassing of isobutene formed by the decomposition remained on the cured surface of the coating. Thus, this method is not satisfactory.